(c) University of Michigan
According to the University of Michigan, it was a bumper year for new car fuel efficiency this year.

The average fuel economy (window-sticker value) of new vehicles sold in the U.S. in December was 23.9 mpg, up 3.8 mpg (or 19%) from the value in October 2007 (the first month that the University of Michigan began monitoring). However, the fuel economy in December was down 0.2 mpg from November, likely reflecting the recent reduction in the price of gasoline. The average fuel economy of all vehicles sold in 2012 was 23.8 mpg, up 1.3 mpg from 2011 and up 2.9 mpg from 2008.

The University of Michigan Eco-Driving Index (EDI)-- an index that estimates the average monthly emissions of greenhouse gases generated by an individual U.S. driver-- stood at 0.79 in October. This value indicates a record improvement of 21% since October 2007, and ties the revised value for September. The EDI takes into account both vehicle fuel economy and distance driven (the latter relying on data that are published with a two-month lag).